19 October 1994 Carbon dioxide jet spray cleaning: mechanisms and risks
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Carbon dioxide (CO2) gas/solid jet sprays have been proposed for replacing ozone depleting cleaning solvents and for on-orbit cleaning of satellite-borne sensors. We have performed experiments to ascertain the mechanisms of molecular contaminant film removal with commercial CO2 gas/solid jet spray devices. Infrared measurements of germanium plates coated with various contaminant films were made before, during, and after cleaning with a CO2 jet spray. The inferred cleaning times and overall cleaning efficiencies combined with the known solubilities of the contaminants in liquid CO2 suggest that multiple cleaning mechanisms occur: physical removal of the film and solvation of the contaminant into the CO2 particle. These mechanisms explain the selectivity in cleaning efficiencies of the CO2 jet spray for different contaminants. We have also measured the electrostatic charging induced by the jet spray on ungrounded substrates, which in some cases, charge up to several kilowatts. The charging results from the difference in work functions of the CO2 and substrate. The work function is an intrinsic material property, therefore, the extent of charging can be reduced, but not eliminated. Environmental factors that affect the charging and the resultant limitations placed on the use of this device are discussed.
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Malina M. Hills, "Carbon dioxide jet spray cleaning: mechanisms and risks", Proc. SPIE 2261, Optical System Contamination: Effects, Measurements, and Control IV, (19 October 1994); doi: 10.1117/12.190153; https://doi.org/10.1117/12.190153

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